Composite wires typically include a matrix material reinforced with substantially continuous, longitudinally extending fibers. Examples of composite wires include a metal or polymer matrix material reinforced with fibers (e.g., carbon and ceramic fibers). The use of some composite wires in overhead electrical power transmission cables is of particular interest. Many embodiments of such wires can provide greater power transfer than traditional transmission cables and have thereby allowed increased power transfer capacity with existing electrical transmission infrastructures.
During installation, transmission cable is typically provided on a supply reel and pulled from the reel over a series of sheaves hanging from suspension towers. Care is taken when pulling or otherwise tensioning the cable over the sheave assemblies to avoid bending the cable to a radius less than the minimum bend radius, as excessive tension while bending the cable can result in damage to the cable core, for example. Generally, the amount of bending that is tolerated decreases as the cable tension increases. The minimum bend strength of transmission cables including composite wires, however, is typically higher than for traditional transmission cables not utilizing composite wires.
Additionally, electrical transmission cable is not available in infinite lengths, and as such a series of electrical transmission cables is periodically connected end-to-end (i.e., spliced) in order to provide a sufficiently long span of cable. It is desirable for splices in an installed electrical transmission cable to be full tension splices. Further, it is desirable to connect ends of a series of cables with full tension splices prior to pulling the transmission cable over the sheave assemblies.
Splices used for conventional electrical transmission cables having steel core wires are typically rigid compression splices formed of aluminum and steel tubing. The rigidity of such compression splices prevents the splices from being pulled over sheaves without a high risk of either permanently bending, deforming, or otherwise causing stress damage to the splice itself or a risk of damaging the spliced cable, for example where it transitions into the rigid splice. In particular, “pinch points,” or other small bending radius points are formed at ends of the rigid splice, thereby giving rise to a high risk of transmission cable damage.
In order to reduce such effects, a splice cover formed of an aluminum tube with rubber bushings at each end of the tube is sometimes disposed over these rigid splices to help reduce damage to the rigid splice and spliced steel core cable. However, this practice is seldom used with steel core cables due to a remaining risk of damage.
More flexible, full tension splices, such as formed-wire type splices, have been used to connect composite wire cables. However, methods of pulling such flexible, full tension splices over sheave assemblies have not previously been recognized or employed. In particular, instead of pulling a flexible, full tension splice over sheaves, unspliced cable is pulled over the sheaves, and later spliced. Other methods of connecting the composite wire cables during installation are employed, such as using temporary wire mesh grips, also described as sock splices, to provide a temporary mechanical connection between lengths of electrical transmission cable while the transmission cable is being strung over the sheave assemblies.
The connections formed using these wire mesh grips are relatively low strength in comparison with rated breaking strengths of the cable itself and do not provide any electrical connection. Additionally, even with this type of wire mesh grip connection, there are limits as to angle, tension, and sheave diameter for which the mesh grip connection and connected lengths of cable can be effectively pulled into position over a sheave assembly. For example, damage to the cable at the edges of the wire mesh grip is possible during installation.
Following positioning of the transmission cable over the sheaves, the wire mesh grips are typically replaced with permanent, full-tension splices used to join the lengths of cable. However, later installation of the splices following positioning of the transmission cable adds installation steps (including additional equipment, time, and other costs) and can be problematic, for example, where the installer does not have the necessary field access required to install a splice mid-span between lengths of cable.